The invention relates to a tubular electric incandescent lamp provided with: a tubular translucent lamp vessel sealed in a vacuumtight manner and having a longitudinal axis, a filament longitudinally arranged in the lamp vessel, a respective metal hood accommodated in a respective cupshaped insulator housing and secured to the ends of the lamp vessel, current supply conductors extending from the filament to a respective metal hood, contact members or lamp bases connected to a respective metal hood and extending through an opening in the respective insulator housing transversely of the longitudinal axis of the lamp vessel to the exterior.
Such a lamp is known from U.S. Pat. No. 2,145,787.
The known lamp has disk-shaped metal hoods fused with the tubular lamp vessel. The metal hoods have a recess in their central parts. The lamp bases or contact members, are each undetachably connected to an insulator housing. At a part located inside the insulator housing they have resilient fingers, which are arranged so that they can engage together the recess of the metal hood. The contact members can then be rotated through an arbitrary angle about the axis of the lamp vessel. A lamp provided on either side with such a contact member is ready to be placed with these contact members in the lamp holders of a luminaire intended thereto.
The known lamp has the disadvantage that, when the lamp is removed from the luminaire, the connection between a contact member and the lamp vessel can be lost, while the connection between the luminaire, and this contact member is maintained. When attempts are then made to remove this contact member from the luminaire, there is a risk of the resilient fingers being touched while they are still live.
Since both contact members have to get into contact with a respective lamp holder of a luminaire, the relative distance of these lamp holders should be adapted to the relative distance of the contact members. However, it has been found that the relative distance of the lamp holders can differ so strongly from the relative distance of the contact members of the lamp that the contact members must be placed in an oblique position with respect to the axis of the lamp vessel in order to be able to arrange these contact members in the lamp holders. There is then a risk of the resilient fingers of the contact members losing their grip on the recess in the metal hood. There is moreover a risk that a metal hood of the lamp can be touched whilst the lamp is in the luminaire and is live.
U.S. Pat. No. 4,751,422, an incandescent lamp of the kind mentioned in the opening paragraph is described, in which
the metal hoods are hollow bodies having a continuous wall and a bottom portion, which abut with their open ends against the lamp vessel and have a collar near their bottom portions, PA1 the contact members each have a prong engaging with clamping fit the continuous wall of the respective metal hood on the side of the collar remote from the bottom portion, and PA1 the insulator housings lock the relevant contact members against radial displacement.
In practical embodiments, the insulator housings of the incandescent lamp according to the said Patent Application comprise a tubular part and a cup-shaped part. The cup-shaped part has a bottom portion and a continuous wall portion. The latter portion may be located with its end remote from the bottom portion within the tubular part. The parts can be undetachably interconnected in different ways, for example by means of glue or ultrasonic vibrations or in a mechanical manner, for example by a snap connection by means of barbed hooks.
In these embodiments, a comparatively large number of parts have to be joined in the last step of manufacturing the incandescent lamp. Thus, the manufacture of the lamp is delayed and also the cost price of the lamp is influenced.